1. Field of the Invention
The present invention relates to a taking lens apparatus. More specifically, the present invention relates to a taking lens apparatus (a main component of a digital camera, video camera, or camera incorporated in or externally fitted to a digital video unit, personal computer, mobile computer, cellular phone, personal digital assistant (PDA), or the like) that optically takes in an image of a subject through an optical system and that then outputs it in the form of an electrical signal by means of an image sensor, and in particular to a taking lens apparatus provided with a compact high-zoom-ratio zoom lens system.
2. Description of the Prior Art
In recent years, as personal computers become increasingly wide-spread, digital cameras, which permit easy capturing of images, have been becoming increasingly popular with individual users. Digital cameras are expected to continue becoming more and more popular into the future as an image data input device. The image quality of a digital camera generally depends on the number of pixels on the solid-state image sensor, such as a CCD (charge-coupled device), incorporated therein. Nowadays, digital cameras for general consumers boast of high resolution over one mega pixels, and are closing in on cameras using silver-halide film in image quality. Accordingly, to cope with high resolution of modern image sensors, high optical performance is sought in taking lens systems. On the other hand, in digital cameras for general consumers, zooming, in particular optical zooming with minimal image degradation, is desired.
However, in taking lens systems, it is difficult to achieve high optical performance and a high zoom ratio simultaneously. In addition, in zoom lens systems for use in digital cameras for general consumers, compactness matters. Various proposals have conventionally been made to meet those conflicting requirements. One such proposal is to divert for a digital camera a zoom lens system originally designed for a lens-shutter camera. Another is, as disclosed in Japanese Patent Application Laid-Open No. H8-248318, disposing a prism between lenses to turn the optical axis and thereby shorten the length of the optical system in the direction of the optical axis of the incident light. This helps make a zoom lens system compact.
It is however difficult to meet the aforementioned different requirements simultaneously with conventionally known zoom lens systems. For example, in a lens shutter camera using silver-halide film, the exit pupil of the zoom lens system used therein is located close to the image plane. Thus, using this zoom lens system in a digital camera makes it impossible to fully exploit the light-condensing performance of the microlenses provided in front of the solid-state image sensor, resulting in extremely uneven brightness between a central and a peripheral portion of the image formed. With conventionally proposed zoom lens systems for digital cameras, it is not possible to move their exit pupil away from the image plane without making the zoom lens systems as a whole larger. The zoom lens system disclosed in Japanese Patent Application Laid-Open No. H8-248318 is compact in the direction of the optical axis of the incident light, but its plus-lead zoom type requires a large front lens element and a large reflecting member, resulting in unsatisfactory compactness.